Iodine is a vital trace mineral that our bodies cannot produce on their own, making it essential to obtain it through our diet or supplements. Naturally present in certain foods and added to others like iodized salt, iodine plays a critical role in producing thyroid hormones. These hormones, thyroxine and triiodothyronine, are crucial for protein creation, enzyme activity, and regulating metabolism. Insufficient iodine can hinder thyroid hormone production, potentially leading to hypothyroidism or hyperthyroidism, conditions associated with various adverse health effects.
Foods naturally rich in iodine include a diverse selection of seafood such as fish and shellfish, alongside dairy products like milk, cheese, and yogurt. Other notable sources are seaweed, iodized salt, eggs, and various nuts, seeds, potatoes, and beans.
Recommended Daily Iodine Intake
Understanding the recommended daily intake of iodine is key to maintaining optimal health. Health organizations have established guidelines to help individuals ensure they are getting enough of this crucial mineral.
Recommended Dietary Allowance (RDA): For adults aged 19 years and older, the RDA for iodine is 150 micrograms (mcg) per day. This requirement increases for women during pregnancy and lactation, with recommendations of 220 mcg and 290 mcg daily, respectively. [1, 2]
Tolerable Upper Intake Level (UL): While iodine is essential, excessive intake can also be harmful. The Tolerable Upper Intake Level (UL) is set at 1,100 mcg per day for adults aged 19 years and older, including pregnant and lactating women. This level represents the maximum daily dose that is unlikely to cause adverse health effects in the general population.
The Importance of Iodine for Health
Iodine’s impact on health spans across different life stages, from infancy to adulthood. Its primary role in thyroid hormone production makes it indispensable for various bodily functions.
Iodine’s Role in Infant and Childhood Development
The demand for thyroid hormones rises during pregnancy, emphasizing the need for increased iodine intake in expectant mothers. Iodine is crucial for the physical growth and brain development of both the fetus and infants. Breast milk naturally contains iodine, and many infant formulas are fortified with it to ensure adequate intake. However, it’s important to note that not all prenatal multivitamins include iodine. The American Academy of Pediatrics recommends that pregnant and breastfeeding women use iodized salt and consider iodine supplements to meet their increased needs. [2] It’s worth noting that high-dose iodine supplements should be approached with caution, as they can sometimes lead to thyroid issues in women.
Iodine deficiency in children, particularly moderate to severe cases, can have serious consequences, including lower IQ and stunted growth. Supplementation with iodine in deficient children has shown to improve both physical and cognitive development.
Iodine and Thyroid Disorders: Hypothyroidism and Hyperthyroidism
Iodine is intrinsically linked to thyroid health. Hypothyroidism occurs when the body doesn’t produce enough thyroid hormone, while hyperthyroidism is characterized by overproduction. Elevated levels of thyroid-stimulating hormone (TSH) can be an early indicator of hypothyroidism, often associated with insufficient iodine intake. Ironically, it can also occur in individuals with a history of iodine deficiency who suddenly consume high doses, such as through supplements. [1]
Goiter, an enlargement of the thyroid gland presenting as a lump in the front of the neck, can be a symptom of both hypo- and hyperthyroidism, as well as excessive iodine intake. It’s important to note that goitrogens, found in cruciferous vegetables, can interfere with iodine absorption, potentially affecting thyroid function and contributing to goiter, especially in those with existing iodine deficiency or hypothyroidism.
Top Food Sources of Iodine
Iodine content in food is influenced by the soil and ocean where plants and animals are raised or grown. Seafood and sea vegetables are generally rich in iodine, with lesser amounts found in fortified foods like bread, cereals, and milk.
To answer the question “What Foods Have Iodine?”, here are some of the top dietary sources:
- Seaweed: Sea vegetables such as nori, kelp, kombu, and wakame are among the richest natural food sources of iodine. The iodine concentration can vary significantly between types of seaweed and even within different batches of the same type. For instance, kelp generally contains much higher iodine levels compared to nori. Regular consumption of even small amounts of seaweed can significantly contribute to your daily iodine intake.
- Fish and Shellfish: Various types of fish and shellfish are good sources of iodine. Cod, tuna (especially canned tuna packed in water), oysters, and shrimp are excellent choices. The iodine content in seafood comes from their absorption of iodine from seawater and their diet. Including a variety of seafood in your diet can help ensure adequate iodine intake.
- Iodized Salt: Iodized salt is table salt that has been fortified with iodine, and it is a significant contributor to iodine intake in many countries. The introduction of iodized salt has been a successful public health measure to combat iodine deficiency. Checking labels to ensure your table salt is iodized and using it in moderation during cooking and seasoning can help meet your iodine needs.
- Dairy Products: Milk, cheese, and yogurt are notable sources of iodine. Cows are often fed iodine-containing supplements, which increases the iodine content in their milk. The iodine levels in dairy products can vary depending on farming practices and regional differences. Consuming dairy products regularly can contribute to overall iodine intake.
- Eggs: Eggs, particularly the yolks, contain moderate amounts of iodine. The iodine content in eggs is influenced by the hen’s diet. Eggs are a versatile and widely consumed food, making them a practical source of dietary iodine.
- Other Sources: While less concentrated than the sources listed above, iodine can also be found in beef liver and chicken. Additionally, infant formula is typically fortified with iodine to meet the nutritional needs of babies.
Iodine Deficiency and Toxicity: Understanding the Imbalance
Maintaining the right balance of iodine is crucial. Both deficiency and excess can lead to health problems.
Iodine Deficiency: Risks and Symptoms
Iodine plays a crucial role in regulating metabolism, the process of converting food into energy for cell function and growth. Iodine deficiency can disrupt this process and impede normal growth and development, particularly concerning for pregnant women and infants. In these vulnerable groups, deficiency can lead to miscarriage, stillbirth, stunted growth, and cognitive impairments affecting reading, writing, communication, problem-solving, and social skills.
In adults, a daily iodine intake consistently below 10-20 mcg can result in insufficient thyroid hormone production, leading to hypothyroidism. This condition can disrupt essential metabolic functions, affecting heart rate, body temperature, and weight management. Goiter, or swelling in the neck, is a common symptom of hypothyroidism.
Other signs of iodine deficiency and hypothyroidism include:
- Persistent fatigue and lethargy
- Muscle weakness
- Increased sensitivity to cold temperatures
- Constipation
- Dry skin and hair
- Unexplained weight gain
Individuals at higher risk of iodine deficiency include those who avoid iodized salt and iodine supplements, pregnant women, vegans who exclude all animal products, and people residing in regions with iodine-poor soil, such as mountainous areas.
Iodine Toxicity: Risks and Symptoms
While iodine deficiency is a concern, excessive iodine intake can also pose health risks. Most healthy individuals tolerate high iodine intakes without adverse effects, as observed in populations with high seaweed consumption like in Japan and Korea. However, individuals with autoimmune thyroid disease or a history of iodine deficiency may be more susceptible to iodine-induced thyroid problems from excess intake. [2, 4]
Excessive iodine can paradoxically lead to both hypothyroidism and hyperthyroidism. Hyperthyroidism due to iodine excess can manifest as increased metabolism, weight loss, rapid or irregular heartbeat, tremors, irritability, fatigue, and excessive sweating. In sensitive individuals, even slightly exceeding the RDA for iodine can trigger hyperthyroidism. [4]
Some studies suggest a link between very high seaweed consumption and an increased risk of certain thyroid cancers, particularly in postmenopausal women, although the exact mechanisms are still under investigation. [2, 3]
Severe iodine poisoning is rare but can occur from extremely high doses, leading to symptoms such as fever, abdominal pain, nausea, vomiting, burning sensations in the mouth, throat, and stomach, and in extreme cases, coma. Children, infants, the elderly, and those with pre-existing thyroid conditions are particularly vulnerable to iodine toxicity and iodine-induced thyroid disorders. [3, 4]
Did You Know?
- In the United States, the primary sources of dietary iodine are iodized salt and milk.
- Iodine supplements can interact negatively with certain blood pressure medications and diuretics, like lisinopril, spironolactone, and amiloride, potentially causing hyperkalemia, a dangerous buildup of potassium in the blood.
- Iodine is a key component in contrast agents used in medical imaging procedures like X-rays and CT scans, enhancing image clarity by improving ray absorption.
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References
[1] National Institutes of Health (NIH). Iodine. Fact Sheet for Health Professionals. https://ods.od.nih.gov/factsheets/Iodine-HealthProfessional/
[2] World Health Organization (WHO). Iodine deficiency in pregnant and lactating women and children under 5 years of age: WHO guidelines. Geneva: World Health Organization; 2018.
[3] Zava TT, момента del Real G, Rose NR. Health implications of high iodine intake. Thyroid. 2017 Nov;27(11):1307-1317.
[4] Leung AM, Braverman LE. Consequences of excess iodine. Nat Rev Endocrinol. 2014 Mar;10(3):136-42.
Last reviewed March 2023
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